1. Field of the Invention
The present invention relates to semiconductor storage devices, and more particularly to a semiconductor storage device which, connected to a host computer, is operated such that a semiconductor memory is divided into a plurality of logical volumes.
One of the requirements for a semiconductor storage device is that the constitution of a logical volume can be modified without stopping the operation.
2. Description of the Prior Art
In a conventional semiconductor storage device operated such that a semiconductor memory is divided into a plurality of logical volumes, the operation of the semiconductor storage device must be stopped and data in the semiconductor memory is saved in a magnetic tape device or the like, before the constitution of the logical volume is modified. Thereafter, the data saved in the magnetic tape device or the like is restored in the semiconductor memory.
A problem with the conventional semiconductor storage device is that an exhaustive operation for modifying the constitution of the logical volumes is necessary when the existing logical volume is to be expanded by newly installing a semiconductor memory, and that each time the modifying operation is carried out, the operation of the semiconductor storage device has to be stopped, and data has to be saved. Another aspect of the problem is that the host computer has to be stopped when the data is to be saved, because the host computer is used in the saving operation.
One approach to solve the problem is that the expanded (newly installed) memory is used as an expanded logical volume, and the expanded logical volume is linked to the existing logical volumes. However, there is a limit to the number of links of logical volumes established. Hence, it is necessary to modify the entirety of the constitution of the logical volumes before the limit for the number of links is reached. Each time the modifying operation is carried out, the operation of the semiconductor storage device must be stopped, and data saving operation must be carried out.